RESUMEN
In this paper, we investigate the dynamics of spherical droplets in the presence of a source-sink pair flow field. The dynamics of the droplets is governed by the Maxey-Riley equation with the Basset-Boussinesq history term neglected. We find that, in the absence of gravity, there are two distinct behaviors for the droplets: small droplets cannot go further than a specific distance, which we determine analytically, from the source before getting pulled into the sink. Larger droplets can travel further from the source before getting pulled into the sink by virtue of their larger inertia, and their maximum traveled distance is determined analytically. We investigate the effects of gravity, and we find that there are three distinct droplet behaviors categorized by their relative sizes: small, intermediate-sized, and large. Counterintuitively, we find that the droplets with a minimum horizontal range are neither small nor large, but of intermediate size. Furthermore, we show that in conditions of regular human respiration, these intermediate-sized droplets range in size from a few µm to a few hundred µm. The result that such droplets have a very short range could have important implications for the interpretation of existing data on droplet dispersion.
RESUMEN
We examine the evolution of a liquid drop on an inclined substrate oscillating vertically. The oscillations are weak and slow, which makes the liquid's inertia and viscosity negligible (so that the drop's shape is determined by a balance of surface tension, gravity, and vibration-induced inertial force). No assumptions are made about the drop's thickness, which extends our previous results on thin drops [Benilov, Phys. Rev. E 84, 066301 (2011)] to more realistic situations. It is shown that, if the amplitude of the substrate's oscillations exceeds a certain threshold value ε(*), the drop climbs uphill. ε(*), however, strongly depends on the thickness of the drop, which, in turn, depends on the liquid's equilibrium contact angle ß[over ¯]. In particular, there is a dramatic decrease in ε(*) when ß[over ¯] exceeds a certain threshold, which means that thick drops climb uphill for a much weaker vibration of the substrate. At the same time, the frequency range of the substrate's vibration within which drops climb uphill becomes much narrower.
RESUMEN
The shell thickness and mass of eggs of the dipper (Cinclus cinclus) collected on streams of different pH in Wales and Scotland were measured. The aluminium, phosphorus and calcium content of their invertebrate prey were also measured. In a regression analysis, significant at p<0.05, stream pH accounted for up to 7% of the variance in shell thickness, with shells decreasing by 2.5% of the overall mean with each unit of pH decline. In the Welsh sample, differences in shell thickness due to pH were small compared with differences between years across all sites. In data pooled between Scotland and Wales, pH accounted for 17% of the variance in egg mass, but a greater proportion (25%) in Scottish eggs alone. Aluminium concentrations in invertebrates showed no relationship with stream pH, but calcium levels in two insect orders increased significantly with pH. Calcium rich prey, such as Gammarus, were found only in circumneutral streams. The importance of calcium in the diet of dippers before and during egg formation is discussed. No evidence that aluminium in prey adversely affected dipper eggs was found.
RESUMEN
Rana temporaria tadpoles were raised to metamorphosis at 6 levels of pH (pH 3.6-6.5) and 2 levels of aluminium (800 and 1,600 µg l-1) at pH 4.4. Treatments involved both chronic and acute exposure to depressed pH. Decreasing pH reduced maximum body size and delayed metamorphosis. Growth was depressed and metamorphosis delayed by 800 µg l-1 Al, and several tadpoles died at foreleg emergence. At 1,600 µg l-1 Al, small tadpoles suffered arrested growth and development and eventually died, while larger tadpoles metamorphosed without delay, though at a very small size. There was no mortality among controls. The levels of pH and inorganic monomeric aluminium measured in the experiments were similar to field levels at a site in Scotland, and it is concluded that individual tadpoles will, in certain types of water body, be adversely affected by both acidity and aluminium. The impact of these factors on populations remains to be determined.
